Electron discharge devices and molybdenum slow wave structures, the molybdenum slow wave structures having grain alignment transverse to the electron path



May 30, 1967 H. i. SCHRAGER 3,322,996

ELECTRON DISCHARGE DEVICES AND MOLYBDENUM SLOW WAVE STRUCTURES, THE MOLYBDENUM SLOW WAVE STRUCTURES HAVING GRAIN ALIGNMENT TRANSVERSE TO THE ELECTRON PATH Original Filed Dec. 17, 1962 HUBERTI.SCHRAGER V ATTORNEY United States Patent ELECTRON DISCHARGE DEVICES AND MOLYB- DENUM SLOW WAVE STRUCTURES, THE M0- LYBDENUM SLOW WAVE STRUCTURES HAV- ING GRAIN ALIGNMENT TRANSVERSE TO THE ELECTRON PATH Hubert I. Schrager, San Francisco, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Continuation of application Ser. No. 245,259, Dec. 17, 1962. This application Oct. 18, 1966, Ser. No. 587,619

4 Claims. (Cl. 3153.5)

This application is a continuation application of my parent application U.S. Ser. No. 245,259 filed Dec. 17, 1962 and assigned to the same assignee as the present invention, now abandoned, of which a divisional application U.S. Ser. No. 581,127 filed Aug. 8, 1966 directed to the method of manufacturing slow wave circuits disclosed therein and herein was filed.

The present invention relates in general to electron discharge devices such as traveling wave tubes and more particularly to molybdenum slow wave structures and a method of making molybdenum slow wave structures for microwave devices such as, for example, traveling wave tubes and the like.

Some of the more useful slow waves structures presently employed in microwave devices such as traveling wave tubes are the contrawound helix and ring and bar structures described in U.S. Patents No. 2,836,758 and No. 2,937,311 by M. Chodorow. The function and operating principles of these structures are well known and adequately described in the above-mentioned U.S. patents and in the literature.

Conventional techniques for manufacturing slow wave structures of the above-mentioned type generally involve costly and time consuming precision grinding and machining operations performed on extruded tubing. A typical ring and bar circuit made from drawn molybdenum tubing required grinding the outer diameter to size, honing the inner diameter to size, grinding the required notches to form the desired slow wave configuration, deburring the part by means of ultrasonic techniques and X-raying the part for fractures. Furthermore, the finished product was still extremely susceptible to breakage due to inclusions in the material acquired during the drawing process and also due to draw marks running the length of the helix. Previously, molybdenum slow wave circuits have been initially shaped with the longitudinal axis of the slow wave device aligned with the longitudinal axis of the molybdenum crystal grain structure. It has been found that tubes fabricated with such grain orientations are relatively brittle, hence quite frangible. The above structural defects coupled with the relatively high cost of manufacture made it imperative to improve existing slow wave structures and methods of making slow wave structures of the above-mentioned type in order to achieve a more rugged structure and tube incorporating such a structure.

The present invention obviates the above-mentioned deficiencies by providing a novel method of manufacturing molybdenum slow wave structures of the above-mentioned type which results in a mechanically superior slow wave structure and additionally results in a more rugged and reliable electron discharge device of the traveling wave type or the like in which said slow wave structure is employed.

The principal object of the present invention is to provide a more rugged, easily fabricated, more reliable and more economical molybdenum slow wave structure.

Another feature of the present invention is to provide a more rugged and economical molybdenum slow wave structure for use in traveling wave tubes and the like.

3,322,996 Patented May 30, 1967 Still another feature of the present invention is to provide a more rugged, reliable and economical microwave electron discharge device of the traveling wave type or the like employing the molybdenum slow wave structure of the aforementioned feature.

Other features and advantages of the present invention will become more apparent upon perusal of the following specification taken in connection with the accompanying drawing wherein:

FIGURE 1 is a fragmentary longitudinal view partly in cross-section of an exemplary traveling wave tube embodying one of the slow wave structures of the abovementioned types.

FIGURE 2 is a perspective view of a punching die showing fiat stock being fed thereto and punched according to the desired slow wave configuration.

FIGURE 3 is a perspective view of a first forming die having the desired slow wave structure positioned therein together with the resultant U-shaped slow wave structure after the first forming operation.

FIGURE 4 is a perspective view of a second forming die having the U-shaped slow wave structure positioned therein together with the resultant cylindrical shaped slow wave structure after the second forming operation.

FIGURE 5 is a perspective view of a firing jig having the cylindrical slow wave structure surrounding a mandrel having an outer diameter equal to the desired inner diameter of the slow wave structure mounted therein together with the resultant perfectly circular annealed part after the firing operation.

FIGURE 6 is a perspective view of a brazing jig having the annealed circular slow wave structure mounted therein showing the brazing material positioned on the closed upwardly directed edges of the formed slow wave structure prior to the brazing operation.

FIGURE 7 shows a perspective view of the finished slow wave structure resulting from the method of manufacture of the present invention.

FIGURE 8 shows an exemplary contrawound helix in fiat form after the stamping, or etching, operation and prior to the forming operation.

FIG. 9 is a perspective view of the V-shaped portions formed at the mutually opposing segments of the cylindrical slow wave structure prior to brazing.

Referring to FIG. 1 there is shown a traveling wave tube of the type shown and described in copending U.S. patent application Ser. No. 20,983 by John W. Sullivan and William L. Rorden and assigned to the assignee as the present application, now Patent No. 3,195,006 issued July 13, 1965.

Briefly, the traveling wave tube 11 comprises a ring and bar molybdenum slow wave structure 12 supported by a series of longitudinally extending sapphire rods 13 or the like to which the slow wave structure is brazed and positioned within a stainless steel tube 14 or the like. A circuit sever to prevent oscillations is shown at 44. Tube 14 is supported at one end by being brazed to steel anode member 15 and at the other end by being brazed to an annular hollow member 16 of wave permeable material such as alumina ceramic or the like. Collector structure 17 forms the termination for a cylinstructures such as the contrawound helix could be positioned therein according to the present invention.

The following description with respect to FIGS. 2-7 will describe a novel and unique method of manufacturing a particular slow wave structure (ring and bar) from a flat sheet of molybdenum. While the ring and bar configuration is shown as a preferred embodiment, the following method of manufacture is equally applicable to the fabrication of other molybdenum slow wave structures such as the contrawound helix or any other circuit configuration capable of being developed into a plane.

In FIG. 2 is shown the preferred first operation employed in fabricating a typical slow wave structure as exemplified by the ring and bar structure. A flat sheet 23 of molybdenum having a transverse grain structure with respect to its longitudinal axis is positioned within a punching die assembly 24 having the desired configuration whereby the preselected portions of the sheet 23 are removed upon actuation of the punch portion 25 of the die 24. The severed parts simply fall through apertures in the bottom of the die corresponding to the dimensions of the portions to be removed. The punching die 24 can be designed to remove a slot such as 26 in one operation or an entire central section 27 in one operation or both 26 and 27 simultaneously or as many slots and central sections as desired in a single operation. As can readily be seen this technique is easily adapted to mass production and is extremely flexible in that by simply choosing the correct die assembly 24 any desired configuration may be produced.

In FIG. 3 there is depicted the first forming die assembly 28 within which the punched part is positioned, as shown, with the upper portion of the forming die actuated to depress the elongated member 29 having curved lower edge portions into a corresponding elongated slot 30 to thereby form the slow wave structure into the proper U- shaped configuration as shown.

The next step is shown in FIG. 4 wherein the second forming operation is performed by forming die assembly 31 by depressing elongated circular bar 32 into the semicylindrical slot 34 in the die assembly 31. This operation forces the U-shaped slow wave structure to move into an upper slot corresponding in shape to the outer surface of the slow wave structure to form a nearly perfect cylindrical structure as shown having a narrow slot 35 extending along the length of the circuit.

The next operation is depicted in FIG. wherein a firing jig 36 is shown. A cylindrical mandrel 37 having an outer surface corresponding to the desired inner surface of the slow wave structure is positioned within the slow wave structure and both are inserted within the somewhat separated semi-cylindrical halves of the firing jig 36 which is then tightened by means of screws 38 and the adjacent opposing surfaces of slot 35 are brought into intimate or at least close contact with the lower edges of the opposing surfaces making contact to form a slight V-shaped slot as best seen in FIG. 9 and the assembly is then fired in a hydrogen furnace at approximately 1000 C. for approximately minutes and then removed. It is to be understood that the V-shaped slot is not mandatory since the braze could easily take with flush matching surfaces in intimate contact. Such surfaces can easily be obtained by siutably shaping the opposing surfaces. The resultant slow wave structure as shown in FIG. 5 is then removed and a perfectly formed and stress relieved ring and bar slow wave structure of molybdenum is formed by the above annealing process.

The final operation is depicted in FIG. 6 wherein the formed and stress relieved ring and bar slow wave structure is positioned in a brazing jig 39 as shown and a mixture of brazing material 40 preferably composed of 43% molybdenum powder and 57% nickel powder mixed with a binder of nitrocellulose glue is applied to the V-shaped slots bounded by the bottom edges of the above-mentioned opposing surfaces now in intimate contact. The

brazing material 40 is applied by any suitable means such as painting or dropping and the assembly is fired in a hydrogen furnace at approximately 1250" C. for approximately 5 minutes. It is to be understood that other metal joining techniques besides brazing such as welding, for example, are contemplated and understood to fall within the scope of the present invention. The resultant structure is shown in FIG. 7 wherein a perfectly formed and stress relieved ring and bar slow wave structure 41 having a seam 43 is depicted.

In FIG. 8 a partially cut-out configuration of a contrawound helix slow wave structure 42 in flattened configuration such as shown in FIG. 2 for the ring and bar configuration is depicted. The above-recited method of fabrication explained with reference to the ring and bar structure made from molybdenum is equally applicable to the fabrication of a contrawound helix slow wave structure made from molybdenum. The above-recited operations are utilized to form a slow wave structure from a fiat sheet of molybdenum approximately .015 in. thick and approximately .973 in. wide and varying in length. Quite obviously the instant invention can be used to fabricate slow wave structures for the complete microwave spectrum.

The initial stamping or punching operation could be performed by conventional electrical discharge techniques or by conventional photoetching techniques to form the desired pattern from flat stock.

It is important to select flat stock and to so align the fiat stock when performing the stamping operation such that the grain structure of the metal will be transverse to the major or longitudinal axis of the finished slow wave structure.

By aligning the grain structure of the molybdenum stock at right angles to the longitudinal axis of the slow wave structure it has been found that the slow wave device has considerably fewer fractures induced in response to radial or transverse forces applied to the structure than a structure wherein the molybdenum crystal longitudinal axis of the stock material is aligned with the longitudinal axis of the slow wave circuit. It has been found that there are pronounced anisotropic ductility properties in standard molybdenum sheet stock, even after firing. The enhanced anisotropic properties have been found to be in the same direction as the grain orientation of the original sheet of molybdenum so that in a slow wave circuit fabricated in accordance with the present invention, as indicated supra, the axis of highest ductility of the finished product is disposed parallel to the external peripheral surface of the slow wave structure and transverse to the longitudinal axis of the slow wave circuit.

The reasons for the anistropic nature of the finished product are not readily apparent from metallurgical considerations, particularly since firing and annealing of a metal destroy its grain structure. In fact, photornicro graphs taken of molybdenum samples similar to those set forth in the present specification indicate that the grain structure is changed from an elongated configuration to a recrystallized equi-axial pattern in response to firing and annealing. In spite of such recrystallization, tests peformed indicate that the fired and annealed molybdenum has anisotropic ductility properties. In particular, fired molybdenum stock was easily bent to an angle of over a diameter rod with the original longitudinal grain orientation at right angles to the rod longitudinal axis. No evidence of a tendency to fracture and good ductility properties were observed. In contrast, any bending of the fired stock from the same sample over a diameter rod with the original longitudinal grain orientation aligned with long axis of the rod caused the molybdenum to be fractured.

It is within the purview of the present invention to utilize other forming techniques to obtain the cylindrical configuration of the slow wave structure such as, for ex ample, the use of a cam die assembly.

Furthermore, it is within the scope of the present invention to fabricate ring and bar contrawound helix structures and any other circuit configurations capable of being developed into a plane which have an axial slot extending the length of the structure such as slot 35 shown in FIG. 4. The fabrication technique of such a structure differs from the above-recited method of fabrication only in that the final brazing operation is eliminated and that an enlarged mandrel 37 would be preferred during the an-- nealing operation, depicted in FIG. 5, in order to maintain the desired slot dimensions during the annealing operation.

It is to be understood that the term stress relieved refers to a condition wherein the structure will retain its shape indefinitely provided it is not subjected to deforming forces.

It is further contemplated that slow wave configurations other than the cylindrical shape depicted in the preferred embodiment such as oblong or rectangular etc. may be constructed by the fabrication techniques of the present invention.

Since many changes could be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the drawings shall be interpreted as illustrative and not in a limiting sense.

I claim:

1. An electron discharge device comprising (a) means positioned at one end of a predetermined path for directing an electron beam along said predetermined path,

(b) means for collecting said electron beam positioned at the other end of said predetermined path,

(c) a metal sheet member forming an integral hollow tubular slow wave structure having a plurality of parallel current flow paths of tape-like cross-sectional configuration positioned along said predetermined path and capable of supporting electromagnetic Wave energy for interaction with said electron beam, said 5 slow wave structure being made of annealed molybdenum having anistropic ductility properties, with the axis of highest ductility lying parallel to the external peripheral surface defined by said slow wave structure and transversely oriented with respect to said predetermined path. 2. The device defined in claim 1 wherein said slow wave structure is of a ring and bar configuration.

3. The device defined in claim 1 wherein said slow Wave structure is of a contrawound helix configuration.

4. A slow wave circuit for high frequency electron discharge devices comprising an elongated cylindrical ring and bar configuration made of a single metal member made of annealed molybdenum having anistropic ductility properties with the axis of highest ductility lying parallel to the external peripheral surface defined by said slow wave circuit and transversely oriented with respect to the longitudinal axis of the slow wave circuit.

References Cited UNITED STATES PATENTS 1,760,560 5/1930 Kranz et a1. 29159.3 2,004,138 6/19-3'5 Story 61: a1. 29-156 2,761,828 9/1956 Eldredge et a1. 2049 2,822,502 2/1958 Sensiper 3l5-3.5 2,937,311 5/1960 Chodorow 3l53.6 2,957,103 10/1960 Birdsall 315-3.6 3,068,432 12/1962 Dohler et a1. 333-31 3,105,285 10/1963 Favre 29-1555 3,192,609 7/1965 -Murata et al. 29-155.5 3,195,006 7/1965 Sullivan et a1. 3153.5 3,201,720 8/ 1965 Bradford et al 33331 FOREIGN PATENTS 963,317 7/1964 Great Britain.

1,013,090 12/ 1965 Great Britain.

HERMAN KARL SAALBACH, Primary Examiner. R. D. COHN, Assistant Examiner. 

4. A SLOW WAVE CIRCUIT FOR HIGH FREQUENCY ELECTRON DISCHARGE DEVICES COMPRISING AN ELONGATED CYLINDRICAL RING AND BAR CONFIGURATION MADE OF A SINGLE METAL MEMBER MADE OF ANNEALED MOLYBDENUM HAVING ANISTROPIC DUCTILITY PROPERTIES WITH THE AXIS OF HIGHEST DUCTILITY LYING 